The present invention relates to bioabsorbable polyesters possessing porous structures and their use in novel polymer-drug formulations. More specifically, this invention relates to the frabrication of tubular drug delivery devices from polycaprolactone or its copolymers with other lactones, said devices possessing walls of defined porosities which can be adjusted by proper selection of the production parameters to yield formulations exhibiting the desired rates of drug release.
U.S. Pat. No. 3,887,699 to Yolles discloses a device for dispersing drugs from a biodegradable polymeric material which is shown to be polylactate. U.S. Pat. No. 4,148,871 to Pitt, et al, discloses the use of biodegradable homopolymers and copolymers of .epsilon.-caprolactone for formulating devices to accomplish the sustained subdermal delivery of drugs. Neither of these references, however, discloses the use or the fabrication of bioabsorbable devices, exhibiting a porous polymer structure. As a consequence of the dense structure of the polymeric component of the disclosed polymer-drug formulations, the application of these devices is limited to drugs of low molecular weight (less than 500 dalton) which in addition must be sufficiently soluble in the encapsulating polymer. In contrast to both the disclosed drug delivery devices, the novel polymer-drug formulations of the present invention utilize porous polymers and, consequently, the applications of these novel devices are not restricted by the molecular weight of the dispensed drug or its solubility in the polymer.
U.S. Pat. Nos. 4,045,418 and 4,057,537 to Sinclair disclose the fabrications of random copolymers of .epsilon.-caprolactone with D,L-lactide and L-lactide, respectively. These patents do not, however, disclose the concept of polymer-drug formulations of the controlled delivery of drugs.
The Netherland Patent Applications Nos. 8202893 and 8202894 to Gogolewski and Pennings disclose the fabrication of porous polyactate and porous polyactate-polyurethane blends and the use of these materials for biodegradable prosthetic devices. the fabrication and the application of porous prosthetic devices derived from polyactate and its blends with polyurethane have been disclosed also in several scientific publications. See for example S. Gogolewski and A. J. Pennings, Makromol. Chem., Rapid. Comm., 3, 839 (1982), 4, 213 (1983); Coll. Polym. Sci., 261, 477 (1983). The disclosures by Gogolewski and Pennings do not include the concept of the controlled release of high molecular weight drugs which is germane to the present invention and are restricted to polylactate and its blends with polyurethanes.